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Dumb Math Question

Are you smarter than a 5th grader?

     
1:38 am on Nov 20, 2007 (gmt 0)

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Well, I'm not. Maybe you are.

Trying to help my kid with his math work. Trying not to look too dumb here. Can one of you WebmasterWorld math wizards help us out?

Problem:

One number is 6 more than another. If the sum of the smaller number and 3 times the larger number is 34, find the two numbers.

1:56 am on Nov 20, 2007 (gmt 0)

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4 and 10?
1:58 am on Nov 20, 2007 (gmt 0)

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One number is 6 more than another. If the sum of the smaller number and 3 times the larger number is 34, find the two numbers.

two equations, two unknowns:
x=y+6
y+3x=34

substitute for x in the second equation and solve for y.
substitute for y in the first equation and solve for x.

1:59 am on Nov 20, 2007 (gmt 0)

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4 and 10?

you get an F for not showing your work!

2:03 am on Nov 20, 2007 (gmt 0)

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-F-

phranque, i am Russian, i do it in my head :),

i had 5+ in math

2:05 am on Nov 20, 2007 (gmt 0)

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I'm sure there is a shorter, more formal way to do this, but here you go. "S" is the small number, "L" is the larger.

Two equations given:
1) L=S+6
2) S+3xL=34

Using equation #1, substitute (S+6) for L in Equation #2:
S+3x(S+6)=34

Convert 3x(S+6) to 3xS + 3x6:
S+3xS+3x6=34

3x6=18:
4xS+18=34

Subtract 18 from both sides of the equation:
4xS=16

Divide both sides of the equation by 4:
S=4

If S=4, and L=S+6, then L must be 10:

Plug the numbers back into equation #2 to test it:
4+(3x10)=34

Jim

2:06 am on Nov 20, 2007 (gmt 0)

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two equations, two unknowns:
x=y+6
y+3x=34

substitute for x in the second equation and solve for y.
substitute for y in the first equation and solve for x.

Let me guess, PHP, SQL & Basic pro or just good at maths?!

2:17 am on Nov 20, 2007 (gmt 0)

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Speaking of Math:

[cosmos.bcst.yahoo.com...]

this link is to the video, i hope its ok

2:19 am on Nov 20, 2007 (gmt 0)

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phranque, i am Russian, i do it in my head :),

i had 5+ in math


when a 5th grader asks for help in math, the worst thing you can do is give him/her the answer (only).

Let me guess, PHP, SQL & Basic pro or just good at maths?!

no php, plenty of sql, no basic of any flavor for decades, plenty of math way back when, kids in school...
2:24 am on Nov 20, 2007 (gmt 0)

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you right about that, sorry
2:29 am on Nov 20, 2007 (gmt 0)

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the F was a joke...
3:03 am on Nov 20, 2007 (gmt 0)

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Surely this is much simpler as you know that one number is 6 less than the higher number you can look for 4 times the higher number knowing without worrying about the lower number until you have the first answer (no need to overcomplicate the logic on this one):

3x + (x - 6) = 34

>> Which simplifies to

4x - 6 = 34

>> move the 6 over (changing the sign)

4x = 34 + 6

>> Add

4x = 40

>> Dividing gives

x = 10

>> Find smaller number

y = x - 6

>> which gives

y = 4

>> Hence (after checking 3*10 + 1*4 = 34)

Larger number = 10
Smaller number = 4

3:15 am on Nov 20, 2007 (gmt 0)

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Now I can look smarter than I really am. WebmasterWorld to the rescue once again. Thanks.
3:22 am on Nov 20, 2007 (gmt 0)

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I agree that it's not good to give a 5th grader the answer to an algebra problem, in addition I don't think you should give them the method. Teaching methods is what the school has done, the homework is evidently designed to stretch the 5th grader's ability to reformulate the problem intuitively. More time (as long as it takes), a mug of coffee, and a room with no distractions are the best way for a student to solve a mathematics problem.
3:57 am on Nov 20, 2007 (gmt 0)

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initialy I thought it backwords though:

34=3(x+6)+x; came up with the lower number first;

4:51 am on Nov 20, 2007 (gmt 0)

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Yahoo answers is my son's friend when I can't help him ;)
5:25 am on Nov 20, 2007 (gmt 0)

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you get an F for not showing your work!

Maybe at school, but surely not in real life :)

6:06 am on Nov 20, 2007 (gmt 0)

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Trying to help my kid with his math work.

sounds like school to me...
3:57 pm on Nov 21, 2007 (gmt 0)

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In the UK we have a TV program called 'Are You Smarter than a 10 Year Old'. While I'm not sure how old a 5th grader is, older than that by the looks of the question, I'm regularly astounded at some people's lack of knowledge of anything.

One question an adult couldn't answer:
Some bloke works for 10 hours, and sleeps for 8. In it's simplest form, what fraction of the day does he work?

Another:
What is the young of a Kangaroo called?

I can't believe people don't know this stuff!

4:15 pm on Nov 21, 2007 (gmt 0)

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While I'm not sure how old a 5th grader is, older than that by the looks of the question,...

a typical 5th grader would be 10-11 years old.
and now that you mention it algebra isn't usually taught in 5th grade - that must be some school.

4:27 pm on Nov 21, 2007 (gmt 0)

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mention it algebra isn't usually taught in 5th grade

Particularly with double unknowns.

5:01 pm on Nov 21, 2007 (gmt 0)

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One question an adult couldn't answer:
Some bloke works for 10 hours, and sleeps for 8. In it's simplest form, what fraction of the day does he work?

Another:
What is the young of a Kangaroo called?


Not being able to perform (fairly) basic math is one problem, not being able to recall (or never having learned) a bit of trivia that isn't critical in real life (unless you're on Jeopardy and that's the question for Final Jeopardy) is another story.

On the other hand, if you lived in Australia and couldn't answer the 2nd question...

[edited by: LifeinAsia at 5:02 pm (utc) on Nov. 21, 2007]

5:31 pm on Nov 21, 2007 (gmt 0)

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algebra isn't usually taught in 5th grade - that must be some school

We got a recommendation spit out by a computer from school that we work on Geometry with our 5th grader. Okeedoke.

And yes, some of the homework my 5th grade has been bringing home looks a lot like Algebra. I think it's supposed to be "guess and check" but some of the kids are using variable substitution because it's quicker.

5:02 pm on Nov 23, 2007 (gmt 0)

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Why not teach your grade 5'er to do Gauss-Jordan Elimination.

Its easy, and your kid will never have a problem solving a series of non-homogenous linear equations again.

1:48 am on Nov 24, 2007 (gmt 0)

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Dabu The Dragon, I assume you're not a programmer? In my opinion, the best way to learn algebra for a kid is to learn to write programmes. Nowhere else will constantly be challenged to write and solve equations of all levels of complexity whilst thoroughly enjoying themselves.

Pick a comprehensive but syntactically simple language such as a BASIC derivative and teach the kid how to build simple apps, games, toys etc. As a childhood hobby it is very engaging and involving and has the side effects of high intellectual stimulation at very minimal ongoing investment compared to most hobbies.

 

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